An acetylene-functional benzoxazine (AFBEN) which was used to modify poly(dimethylsilyleneethynylenephenyleneethynylene) (DMSEPE) was synthesized by a solventless procedure. The modified resins (DMSEPE/AFBEN) were obtained by blending DMSEPE and AFBEN in different amount. The thermopolymerization of DMSEPE/AFBEN resins were investigated by DSC technique. The dynamic mechanical analysis showed that the storage modulus (E) of the cured DMSEPE/AFBEN resin containing less than 30 wt% AFBEN did not decrease at the temperature lower than 500 A degrees C. When the AFBEN loading increased from 20 to 100 wt%, a decrease in glass transition temperature from 523 to 342 A degrees C was observed. The thermal stability of the cured DMSEPE/AFBEN resins was determined by thermogravimetric analysis (TGA) in N-2 and air. The TGA results showed the cured DMSEPE/AFBEN resins had good thermal stability. The carbon fiber (T700) reinforced DMSEPE/AFBEN composites exhibited excellent mechanical properties (flexural strength: 1,694 MPa) at room temperature and high strength remaining of 76% at 300 A degrees C.